Continuing effort is being employed to provide continuous measurement while drilling ("MWD") of the earth to improve the safety, efficiency, and economy of drilling. The drilling of deep oil wells, often to depths of 2 to 4 miles below the surface, generally requires long time periods of from 3 to 6 months because of the many time consuming problems that often arise while drilling. Since deep drilling land rigs presently cost from $5,000 to $25,000 each day; and floating offshore rigs cost from $25,000 to $100,000 each day, the need for minimizing or avoiding many difficulties and shortening the drilling time is evident.
The extensive time and great expense of drilling can be significantly reduced and many problems avoided if the driller is able to continually monitor conditions at the drill bit and at the hole bottom as the drilling progresses. Having such information, the driller can improve the efficiency of the drilling; monitor the direction of the drilling and location of the drill bit; monitor the bottom hole temperatures and pressures to avoid blowouts; and obtain the lithology and other characteristics of the well formations in which the drill bit is operating.
At present a number of methods and apparatus have been used, or attempted, in an effort to satisfy this important need.